Tuesday, October 2, 2007

One for Ripley's

Some bolide issues: the object was luminescent and observable just before impact. Usually meteors become invisible as they approach both because their hot exteriors burn off and because their near-earth velocity is so fast that they are not visible to the naked eye.

A local report indicates that the object streaked in at midday, at 15 minutes before noon, which accounts for an ability to see a smoky tail, but not for an ability to detect something arriving at typical meteor speed.

However, Carancas is in the Andes, so perhaps the altitude was high enough so that the burn process hadn't been completed. I couldn't find the elevation, but nearby Lake Titicaca has an altitude of 3827 meters.

It is certainly true that there was once serious concern about crashes of Soviet nuclear-powered satellites. A museum in New South Wales owns fragments of a Soviet satellite. In 2003, there was worldwide alarm as fragments of the 1400-kilogram BeppoSAX research satellite rained down over equatorial regions, with a 1/200 probability of striking a human victim.

Plugging in numbers to crater expert Jay Melosh's crater calculator gives energy results of between 200 million to 300 million joules for the 13-meter wide crater in Peru. Ronald Woodman, director of the Peru Geophysics Institute, was quoted as saying the impact had a 1.5 seismic scale reading. A 1.5 Richter reading is equivalent to 320 pounds of TNT -- a typical early WW2 bomb blast -- which translates to 669 million joules.

Collectively, 400 kilograms worth of debris reached earth after the 1400-kg BeppoSAX orbiter broke up. The object that landed in Peru had a mass in the vicinity of 11 kilograms (25 pounds), according to numbers I plugged into the crater calculator. An 11-kg satellite fragment is conceivable, but I am unsure what altitude to use to try to estimate terminal velocity. That is, the ratio of the object's mass to the crater diameter will vary according to kinetic energy, and the kinetic energy of satellite debris might be quite different from that of meteor fragments.

Another question is whether the outer shell's heat combined with the impact energy was enough to bring hundreds -- probably thousands -- of liters of groundwater to a boil, releasing noxious steam, possibly tainted by hydrogen sulfide, which is fairly often found mixed with groundwater.

It seems plausible that if an aerial bomb struck subsurface water, it might release a burst of steam. However, thousands of bombs fall without triggering underground steam vents. (And of course at high altitudes it takes less heat to boil water and release steam.)

Future reports by meteor experts should prove interesting. If down the road there is a peculiar lack of interest by experts, then we'll know it was no meteor.

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